The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Plasma etching is frequently used in, for example only, semiconductor fabrication. In plasma etching, ions are accelerated by an electric field to etch exposed surfaces on a substrate. The electric field is generated according to RF power signals generated by a radio frequency (RF) generator of an RF power system. The RF power signals generated by the RF generator are precisely controlled to effectively perform the plasma etching. Plasma can also be used for deposition of thin films. In one example, a sputtering process can deposit metals or insulators using a target of the material to be deposited. Deposition can also be affected using plasma enhanced chemical vapor deposition for semiconductor materials such as amorphous silicon and dielectrics such as silicon nitride. In each case, the plasma electrical parameters must be monitored and controlled for optimum throughput and process repeatability.
An RF sensor placed at the plasma can be expensive or impractical to realize due to the highly reactive nature of the load. Temperature variations at the plasma chamber can also make it very difficult to realize an accurate RF sensor at the plasma load. Finally, the high RF noise content at the plasma can make it very difficult to transmit high speed, real-time measurements of the plasma RF parameters to an external control or monitoring system.
An RF power system may include an RF generator, a matching network, and a load, such as a plasma chamber. The RF power signals are used to drive the load to fabricate various components including, but not limited to, integrated circuits (ICs), solar panels, flat panel displays (FPD), compact disks (CDs), and/or digital versatile (or video) discs (DVDs). The load may include any of a number of elements or devices driven by an RF signal, including, but not limited to, the plasma chamber.
The RF power signals are received at the matching network. The matching network matches an input impedance of the matching network to a characteristic impedance of a transmission line between the RF generator and the matching network. This impedance matching aids in maximizing an amount of power applied to the matching network in a forward direction toward the plasma chamber (“forward power”) and minimizing the reflected power back from the matching network to the RF generator (“reverse power”). Impedance matching also assists in maximizing forward power output from the matching network to the plasma chamber.
The RF power system may also include a virtual sensor arranged to estimate load characteristics in a high-speed, real-time fashion. For example, the virtual sensor may determine a load voltage and a load current based on a mathematical relationship between known electrical characteristics of the RF power system.